Conventional electrophotographic image-forming devices such as laser printers that employ a nonmagnetic, single-component developing method generally include a photosensitive drum on which electrostatic latent images are formed, and a developer cartridge for tribocharging and supplying toner to the photosensitive drum in order to develop the electrostatic latent image formed thereon.
One such developer cartridge disclosed in Japanese Patent Application Publication No. 2000-275948 includes a toner-accommodating chamber for accommodating the toner, and a developing chamber for accommodating a supply roller, a developing roller, and a thickness-regulating blade. A partitioning wall in which an opening is formed divides the developer cartridge into the toner-accommodating chamber and the developing chamber.
This type of developer cartridge also includes an agitator disposed in the toner-accommodating chamber for stirring toner therein. The toner stirred by the agitator is discharged toward the developing chamber through the hole formed in the partitioning wall. The supply roller supplies the discharged toner onto the developing roller while the toner is tribocharged between the two rollers. The thickness-regulating blade scrapes off excess charged toner carried on the developing roller so that the developing roller carries a thin layer on the surface thereof.
A developing device disclosed in Japanese Patent Application Publication No. 2000-250296 includes transparent windows provided at opposing two sides of the toner-accommodating chamber for detecting the amount of residual toner. A cleaning member is further provided on the agitator for cleaning the windows.
A developer cartridge disclosed in Japanese Patent Application Publication No. 2005-24811 supports the shaft of the agitator with a support part having a hollow groove part and a restricting part, the hollow groove part having a guiding portion and a deepest portion. When assembling the agitator, the shaft of the agitator is guided downward along the guiding portion of the hollow groove to the deepest portion, passing over the restricting part, and is maintained in the deepest portion by the restricting part.
The above-described conventional developer cartridges have various disadvantages. One disadvantage is that the charged excess toner that the thickness-regulating blade scrapes off the surface of the developing roller accumulates in the developing chamber and sometimes returns to the toner-accommodating chamber. As the ratio of previously charged toner to uncharged toner increases, charge control becomes difficult when tribocharging the toner between the supply roller and the developing roller, leading to a decline in image quality. Therefore, it is desirable to supply as much of the toner that has been previously charged for development as quickly as possible.
Another disadvantage is that the number of parts required for fixing the cleaning member to the agitator increases, making the assembly process more complex. Further, it is difficult to cleanly peel off the cleaning member from the agitator for recycling when the cleaning member has been fixed with double-sided tape.
With the above-described structure for supporting the shaft of the agitator, there is a danger that the shaft could become damaged when sliding over the restricting part due to a large load being applied to the shaft when the shaft flexes.
Still another disadvantage is that by forming the opening in the casing of the developer cartridge described above for exposing the developing roller, the peripheral edges of the opening are inevitably weaker. Hence, when the user grips the casing near the opening when mounting or removing the developer cartridge, the casing deforms (flexes), which may cause damage to the developing roller or force toner out through a gap formed between the developing roller and the casing.